EM schematic reading guide
Every EM game included a schematic diagram when leaving the factory. Because EM games are
now tens of years old, the diagrams are often lost or found their way into some repairmans
collection. Many times can another games schematic diagram from the same timeframe be helpful,
because there were much similarities between games. However, if you are troubleshooting a
game specific feature, it would be nice to have a schematic available. But, it helps only
if you know how to read it!
A repairman does not have to memorize every schematic. It is sufficient to know how to read
them and recognize different parts and circuits. The information presented here lets you
understand every schematic and make necessary adjustments and repairs in EM pinballs.
These are probably clear for everyone. Relay and solenoid coils do not differ in their drawing
symbols. Sometimes the lamp symbol includes a little loop inside representing the filament.
Electronic hobbyists may wonder the switch symbol. It looks just like capacitor! Anyway these symbols
are frequently used in relay diagrams not only in pinball schematics. A closing switch, that connects
when actuated, is drawn as two parallel lines. An opening switch has a transverse line over the symbol.
These can be connected to get a changeover switch or other multiple switches.
An important part in a pinball machine is the score motor. It has a large amount of switches in several
different levels operated by motor cams. Motor operated switches are drawn with a circle around the switch
symbol. Schematic diagrams are usually drawn with the motor at zero (home) position, and the switch symbol
is marked with a letter for the level (height) and a number for the switch position. After 0 comes 1, and so on
Switches and coils
Score motor switches
Score motor switches are in multiple levels and positions. The level is marked by a letter and the position by a number.
Remember that the switches are drawn at the motor zero position. Then a switch closing at zero is drawn with
an opening switches symbol because it is "normally" closed. Correspondingly switch closing at position 5 is drawn as
closing switch, because it is "normally" open. "Normally" means here the motor being at zero position.
Wire colors are marked in schematics with letters or numbers. Usually the wires
have two colors, one for background, one for a stripe or dots. Those of us who
memorize electronic components color codes, may be a little disappointed to notice
the EM schematic color numbers are totally different! Fortunately different
manufacturers used same numbers, and often the colors are marked in plain text.
The first number is the wires background color. The second number or letter
is the color of stripes or dots. The codes are not always used, sometimes
the color is in plain English.
Y = yellow wire
B-BLU = black wire with blue stripe
15 = red wire with white stripe
On old machines the wire colors might be faded. Especially red color has a tendency
to fade to gray or even white! But when you open the wire bunch a bit, you can usually
see the original color from an unfaded spot.
Real life fault and fixing
The bell rings when scoring ten points, but not with 100 points. Everything
else seems to work. Schematic shows that the bell should ring both with 10
and with 100 points scoring:
Looking at the machine, it is found out that the 100 point score reel does work.
This tells us that the 100 point relay is pulling. What is left to check, is the
black/blue wire between bell and relay, and the relay switches.
Try connecting the bell solenoid black/blue wire with a test jumper lead
to the yellow wire at 100 point relay switch. If the bell rings, problem must
be with relay switch. If it doesn't ring there must be a cut wire between
100 point relay and the bell.